Conventionally, there have been known various types of gas-pressurized writing instruments,which, with a compressed gas sealed in the barrel cylinder, force out ink therefrom by making use of the pressure of the gas. This gas-pressurized writing instrument enables smooth writing, and writing in an upward position, (with an ordinary ball-point pen, air is sucked from the writing point, as a result, ink flows backwards) because a force for pushing the ink out is exerted by the compressed gas therein.
Various types of the gas-pressurized writing instruments have been proposed.
For example, Japanese Utility Model Application Laid-open Sho 58 No. 120084 discloses a double-fold structure, as shown in FIG. 2, in which a pressure check cylinder is arranged outside an ink storage tube and a compressed gas is sealed in the tube. In writing, the compressed gas provides the function of pushing out the ink, producing smooth writing sensation and enabling writing in an upward position, writing in water, or in a weightless state or under other conditions (conventional example 1).
In the conventional example 1, however, the ink storage tube is arranged to stick out from the plug and be in contact with the outside air. Since the compressed gas also permeates through the ink storage tube to the outside, there is a fear that the compressed gas will escape to the outside via the ink storage tube. Therefore, it is necessary to select a material through which the compressed gas hardly permeates, for that of the ink storage tube.
Further, the ink storage tube should have resistance to ink for storage of ink therein.
Though provision of a transparent ink storage tube makes it possible to monitor the remaining amount of ink from the outside, selection of a material under the above conditions for prevention against permeation of the compressed gas and possession of resistance to ink, generally entails difficulties such that the ink storage tube becomes large in wall thickness. Further, the selection becomes extremely difficult if formability is considered and also clear drain performance or the property of causing ink not to adhere to the inner wall of the ink storage tube is wanted, so as to maintaining the ink storage tube clear after ink consumption. When clear drain performance needs to be kept, polypropylene (PP) that presents high permeability to gas has been used.
Japanese Utility Model Application Laid-open Sho 57 No. 121575 also discloses a gas pressurized ball-point pen having a similar double-folded tube, producing smooth writing sensation and enabling writing in an upward position (conventional example 2).
However, also in this conventional example 2, the ink storage tube is arranged so as to stick out of the barrel cylinder, and ink is stored in the ink storage tube. In the conventional example 2, the projected ink storage tube is covered with a holder, but this holder merely covers the front end of the ink storage tube. Further, in consideration of the use of a thread for fixture, ambient air is allowed to easily permeate, which practically means that the ink storage tube is put in direct contact with the outside air. There is a method of sealing by using a sealing material, but is it markedly difficult to select a material which is greasy and has high gas permeability.
Accordingly, in the conventional example 2, selection of a material that meets the above same conditions as in the conventional example 1, i.e., prevention against permeation of the compressed gas and possession of resistance to ink, generally entails difficulties. Further, the selection becomes extremely difficult if clear drain performance, formability and transparency are considered.
The basic configuration of a gas-pressurized ball-point pen as one kind of the gas-pressurized writing instruments is composed of a point assembly for a writing point, an ink storage tube that is connected to the point assembly and stores ink and compressed gas therein, and a tail plug disposed at the rear end of the ink storage tube. For the ink storage tube, several techniques using transparent resin so as to permit the remaining amount of ink therein to be monitored have been disclosed. However, some cases depending on the used resin suffer the gas leakage problem. Specifically, there occurs the problem in that the compressed gas permeates through the resin and leaks out from the interior of the ink storage tube to the outside.
In view of the problems in the conventional art, it is therefore an object of the present invention to provide a gas-pressurized writing instrument and a writing instrument refill, which can prevent gas leakage with a simple configuration and which is advantageous in appearance. It is also an object of the present invention to provide a gas-pressurized writing instrument and a writing instrument refill, which can prevent gas leakage with a simple structure of a fewer number of parts.